Chapter 11: Problem 38
Show that \(\vec{A} \cdot(\vec{A} \times \vec{B})=0\) for any vectors \(\vec{A}\) and \(\vec{B}\).
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Chapter 11: Problem 38
Show that \(\vec{A} \cdot(\vec{A} \times \vec{B})=0\) for any vectors \(\vec{A}\) and \(\vec{B}\).
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Vector \(\vec{A}\) points \(30^{\circ}\) counterclockwise from the \(x\)-axis. Vector \(\vec{B}\) has twice the magnitude of \(\vec{A}\). Their product \(\vec{A} \times \vec{B}\) has magnitude \(A^{2}\) and points in the negative z-direction. Find the direction of vector \(\vec{B}\).
As an automotive engineer, you're charged with redesigning a car's wheels with the goal of decreasing each wheel's angular momentum by \(30 \mathrm{~s}\) for a given linear speed of the car. Other design considerations require that the wheel diameter go from \(38 \mathrm{~cm}\) to \(35 \mathrm{~cm}\). If the old wheel had rotational inertia \(0.29 \mathrm{~kg} \cdot \mathrm{m}^{2}\), what do you specify for the new rotational inertia?
Why is it easier to balance a basketball on your finger if it's spinning?
Biomechanical engineers have developed micromechanical de- Bio vices for measuring blood flow as an alternative to dye injection following angioplasty to remove arterial plaque. One experimental device consists of a 290 - \(\mu \mathrm{m}\)-diameter, \(2.3\)-\mum-thick silicon rotor inserted into blood vessels. Moving blood spins the rotor, whose rotation rate provides a measure of blood flow. This device exhibited an \(830-\) rpm rotation rate in tests with water flows at several meters per second. Treating the rotor as a disk, what was its angular momentum at \(830 \mathrm{rpm}\) ? (Hint: You'll need to find the density of silicon.)
A tumtable of radius \(15 \mathrm{~cm}\) and rotational inertia \(0.0115 \mathrm{~kg} \cdot \mathrm{m}^{2}\) is spinning freely at \(32.0 \mathrm{rpm}\) about its central axis, with a \(20.5-\mathrm{g}\) mouse on its outer edge. The mouse walks from the edge to the center. Find (a) the new rotation speed and (b) the work done by the mouse.
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